Electroplating bath for depositing tin or tin alloy with brightness

ABSTRACT

An electroplating bath for depositing tin or a tin alloy with satisfactory brightness, which comprises a mother bath of a pH-value ranging from 4 to 8 and containing citric acid or its salt, an ammonium salt and a water-soluble polymer as a brightener. The bath may further comprise an aldehyde compound as a co-brightener.

The present invention relates to an electroplating bath for depositingtin or a tin alloy with brightness, and more particularly to such a bathcontaining citric acid or its salt and an ammonium salt.

The electrodeposition of tin or the tin alloy has widely been employedto protect steel or the like metal material from corrosion, or to givesoldering ability to or improve the same of various materials.

For tin electroplating, hitherto, an acidic bath such as sulfuric acidbath or a basic bath such as sodium hydroxide bath has conventionallybeen employed. When the sulfuric acid bath is used, however, ahomogeneous electrodeposition of tin can not be attained. In order toovercome this defect, a relatively large amount of surface active agentshould be added in the bath but this causes bubbling in the bath so asto adversely affect on the plating efficiency and working environment.When the sodium hydroxide bath is used, the bath must be heated to about70° C. to be similarly bubbled which causes the same defects. In thisbath, further, the ionized tin in the bath is of tetravalency so that ahigher current efficiency can not be attained.

For tin alloy electroplating, the bath containing sulfate,pyrophosphate, borofluoride, sodium stannate, alkali cyanide, gluconateor the like have been proposed. Among those, the sulfate, borofluorideand alkali cyanide baths require a special treatment for making sameharmless, when discharged as waste liquid. The pyrophosphate,borofluoride, alkali cyanide and gluconate baths have a disadvantagethat the composition of plated alloy is adversely varied in a relativelywide range due to fluctuation of current density during theelectroplating. Further, borofluoride, alkali cyanide and sodiumstannate baths do not show a desired high plating efficiency.

In order to overcome the disadvantages as referred to, a bath containingcitric acid or its salt and an ammonium salt has been proposed (see, forinstance, USSR Inventor's Certificate No. 293,876).

In the printed specification for said USSR Inventor's Certificate, thereis a disclosure that dextrine and gelatine are added as brighteners toattain a finer and crystalline tin-zinc alloy deposition with abrightness. However, the "brightness" to be attained by this Inventor'sCertificate process is of the degree "dull" or "mat" among thebrightness degrees comprising bright (mirror bright), semi-bright, dull,mat and dendrite.

In order to improve the brightness, one of the present inventors hasproposed together with others a brightener for tin-zinc alloyelectroplatings, which is a water-soluble polymer obtained by reactingan aliphatic amine with an organic acid ester and then further reactingthe reaction product with phthalic acid anhydride, or adding to thefinal reaction product an aromatic aldehyde as a co-brightener (Jap.Pat. Appln. No. 148 687/1974 which was early opened under the number of75 632/1976). The brightener is advantageous in attaining a "bright" or"semi-bright" tin-zinc alloy electroplating regardless of a kind of themetal to be plated or an electroplating bath to be employed. Thebrightener, however, has a practical disadvantage that the range ofworking current density required during the electroplating is relativelynarrow.

Therefore, a principal object of the present invention is to obviate andovercome the disadvantages referred to.

A specific object of the present invention is to provide anelectroplating bath which contains citric acid or its salt and anammonium salt and can commonly be employed for depositing tin andtin-alloys with satisfactory brightness.

Another specific object of the present invention is to provide anelectroplating bath for tin and tin-alloys, which can be employed in awide range of current density and more particularly is excellent inworking efficiency at a higher current density.

A still other specific object of the present invention is to provide anelectroplating bath for tin and tin-alloys, which, in case of thetin-alloy plating, provides a well plated coating having a substantiallyuniform composition, even if the current density fluctuates during theworking.

According to the invention, the above objects and other objects to beappreciated by fully understanding the invention can be attained byadding to tin or tin-alloy mother bath of a pH value ranging from 4 to 8which contains citric acid or its salt and an ammonium salt, abrightener comprising a water-soluble polymer selected from the groupconsisting of a polyoxyethylene, a derivative thereof and a reactionproduct of an epoxy compound with ethylene glycol, propylene glycol orglycerine.

In addition to the water soluble polymer, at least one aldehyde compoundmay be added as a co-brightener. As the aldehyde compounds,formaldehyde, acetaldehyde, propionaldehyde, glyoxal, succindialdehyde,caproaldehyde, aldol or the like aliphatic one and benzaldehyde,p-tolualdehyde, salicylaldehyde, veratraldehyde, anisaldehyde,piperonal, vanillin or the like aromatic one my be employed solely or asa mixture thereof. These aldehyde compounds themselves do not show anyeffect as the brightener when using either solely or in the form of amixture thereof but serve to give a superior brightness to be classifiedas "bright" or "mirror bright" to the tin or tin-alloy electrodepositionwhen the same is used in combination with the water soluble polymer asmain brightener. In this connection, please note that if no aldehydecompound is added to the electroplating bath, tin or tin-alloy film tobe deposited on a base material assumes a brightness classified as"semi-bright" or "dull".

As the polyoxyethylenes and the derivatives thereof, there are compoundsrepresented by the following formulae in which n₁, n₂ and n₃ areintegrals showing polymerization degree ranging from 20 to 200, from 10to 100 and from 5 to 50°, respectively. ##STR1##

The polyoxyethylene or its derivative as the brightener is added to themother bath in an amount of 1 to 5 g/l.

As the epoxy compounds, there are the compounds represented by followingformulae wherein R represents a lower alkyl radical. ##STR2##

The reaction between the epoxy compound and ethylene glycol, propyleneglycol or glycerine can be carried out by combining the both compoundsand heating the mixture at a temperature of 30° to 120° C. under theatmospheric. The mol ratio between the epoxy compound and the otherreactant depends on the number of epoxy radical in the former compound.In case mono-epoxy compound, ethylene glycol, propylene glycol orglycerine is employed in same mol amount with the epoxy compound but incase of di-epoxy compound, said other reactant is used in double molamount. A catalyst of BF₃ or SnCl₄ may be employed to decrease thepolymerization temperature or required reaction time period.

The reaction product as the brightener is added to the mother bath in anamount of 1 to 2 g/l.

The lower limits for the both type brighteners show an amount requiredfor providing "dull brightness", respectively. The excessive addition ofthe brightener does not give any bad influence but is meaningless forimproving the brightness.

The aldehyde compound as co-brightener is added to the mother bath in anamount of 0.1 to 0.5 g/l. The excessive addition does not give any badinfluence but is meaningless.

It is preferable to carry out the electroplating at a bath temperatureof 10° to 40° C. and current desity of 0.1 to 6 A/dm². When the platingbe carried out outside said current density range, the deposited tin ortin-alloy will be sponge like or assume a dull or less brightness.

The invention will now be further explained in reference to examples.

EXAMPLES 1 TO 26

In each Example, any one of the following electroplatings was carriedout.

    ______________________________________                                        1)    Tin Plating                                                                   Anode: Sn plate                                                               Composition of mother bath:                                                   SnSO.sub.4              50 g/l                                                Ammonium citrate        100 g/l                                               (NH.sub.4).sub.2 SO.sub.4                                                                             80 g/l                                                30% aqueous solution of ammonia                                                                       50 g/l                                                pH of bath: 5.0                                                         2)    Tin-Zinc Plating                                                              Anode: Sn--Zn (75:25) alloy plate                                             Composition of mother bath:                                                   SnSO.sub.4              38 g/l                                                ZnSO.sub.4              36 g/l                                                Citric acid             110 g/l                                               (NH.sub.4).sub.2 SO.sub.4                                                                             70 g/l                                                30% aqueous solution of ammonia                                                                       80 g/l                                                pH of bath: 6.0                                                         3)    Tin-Lead Plating                                                              Anode: Sn--Pb (65:35) alloy plate                                             Composition of mother bath:                                                   Sn(OOCCH.sub.3).sub.2   33 g/l                                                Pb(OOCCH.sub.3).sub.2   15 g/l                                                NH.sub.4 (OOCCH.sub.3).sub.2                                                                          50 g/l                                                30% aqueous solution of ammonia                                                                       50 g/l                                                pH of bath: 6.0                                                         4)    Tin-Cobalt Plating                                                            Anode: Sn--Co (70:30) alloy plate                                             Composition of mother bath:                                                   SnSO.sub.4              26 g/l                                                CoSO.sub.4 . 7H.sub.2 O 30 g/l                                                Citric acid             100 g/l                                               (NH.sub.4).sub.2 SO.sub.4                                                                             70 g/l                                                pH of bath: 6.0                                                         5)    Tin-Silver Plating                                                            Anode: Sn--Ag (80:20) alloy plate                                             Composition of mother bath:                                                   SnSO.sub.4              36 g/l                                                Ag(OOCCH.sub.3).sub.2   10 g/l                                                Ammonium citrate        90 g/l                                                NH.sub.4 (OOCCH.sub.3).sub.2                                                                          40 g/l                                                30% aqueous solution of ammonia                                                                       40 g/l                                                pH of bath: 5.5                                                         6)    Tin-Copper Plating                                                            Anode: Sn--Cu (70:30) alloy plate                                             Composition of mother bath:                                                   SnSO.sub.4              22 g/l                                          CuSO.sub.4                                                                          25 g/l                                                                        Ammonium citrate        100 g/l                                               (NH.sub.4).sub.2 SO.sub.4                                                                             80 g/l                                                30% aqueous solution of ammonia                                                                       75 g/l                                                pH of bath: 6.2                                                         ______________________________________                                    

Other tems for carrying out the electroplatings were as follows.

Current charged: 1 A

Current charging time period: 10 min.

Electroplating temperature: 25°±1° C.

Cathode: degreased and cleaned Fe plate (6.5×10×0.3 cm)

Size of Anode: 6.5×6.0×0.5 cm

In Examples 15 to 26, the used brightener is designated by symbols EP-1to 8 which were prepared by the processes shown below.

(1) EP-1

A water-soluble polymer synthesized by heating the following compoundsat 60° C. in the presence of BF₃ as catalyst. ##STR3##

(2) EP-2

A water-soluble polymer synthesized by heating the following compoundsat 80° C. in the presence of BF₃ as catalyst. ##STR4##

(3) EP-3

A water-soluble polymer synthesized by heating the following compoundsat 60° C. in the presence of BF₃ as catalyst. ##STR5##

(4) EP-4

A water-soluble polymer synthesized by heating the following compoundsat 80° C. in the presence of BF₃ as catalyst. ##STR6##

(5) EP-5

A water-soluble polymer synthesized by heating the following compoundsat 90° C. in the presence of BF₃ as catalyst. ##STR7##

(6) EP-6

A water-soluble polymer synthesized by heating the following compoundsat 60° C. in the presence of BF₃ as catalyst. ##STR8##

(7) EP-7

A waater-soluble polymer synthesized by heating the following compoundsat 80° C. in the presence of BF₃ as catalyst. ##STR9##

(8) EP-8

A water-soluble polymer synthesized by heating the following compoundsat 90° C. in the presence of SnCl₄ as catalyst. ##STR10##

Results are shown in the following Table.

    __________________________________________________________________________                                                   Current                        Example                                                                            Mother                            Aldehyde                                                                              Density                        No.  Bath   Brightener                 Compound                                                                              (A/dm)                                                                             Brightness                __________________________________________________________________________                                           veratraldehyde                         1.   tin plating                                                                          HO(CH.sub.2CH.sub.2O) .sub.nH                                                                            (0.5 g/l)                                                                             0.1-2                                                                              bright                         bath                              glyoxal                                            n = 100                    (0.1 g/l)                                                                             0.1-2                                                                              bright                                5 g/l                      none    0.1-2                                                                              semi-bright                                                      anisaldehyde                           2.   tin plating bath                                                                      ##STR11##                 (0.2 g/l)                                                                             0.5-4                                                                              bright                                n.sub.1 = 20               formaldehyde                                       n.sub.2 = 50               (0.1 g/l)                                                                             0.5-4                                                                              bright                                2 g/l                      none    0.5-4                                                                              semi-bright                                                      benzaldehyde                           3.   tin-zinc                                                                             HO(CH.sub.2CH.sub.2O) .sub.nH                                                                            (0.2 g/l)                                                                             0.1-1                                                                              bright                         plating bath                      p-tolualdehyde                                     n =  100                   (0.1 g/l)                                                                             0.1-1                                                                              semi-bright                           5 g/l                      none    0.1-1                                                                              dull                      4.   tin-zinc plating bath                                                                 ##STR12##                 veratraldehyde  (0.5                                                                  0.2-2                                                                              semi-bright                           n = 100                    piperonal                                                                             0.2-2                                                                              semi-bright                           2 g/l                      (0.5 g/l)                                                                     none    0.2-2                                                                              dull                      5.   tin plating bath                                                                      ##STR13##                 glyoxal (0.1 g/l)                                                                     0.5-4                                                                              bright                                                           aldol                                                                         (0.1 g/l)                                          n = 100                    salicylaldehyde                                                                       0.2-2                                                                              bright                                2 g/l                      (0.1 g/l)                                                                     none    0.5-4                                                                              semi-bright               6.   tin-zinc plating bath                                                                 ##STR14##                 acetaldehyde  (0.1                                                                    0.1-2                                                                              semi-bright                                                      piperonal                                                                     (0.5 g/l)                                                                             0.1-2                                                                              bright                                n = 50                                                                        2 g/l                      none    0.1-2                                                                              dull                                  C.sub.3 H.sub.7NH(CH.sub.2CH.sub.2O)  .sub.nH                                                            veratraldehyde                                                                (0.5 g/l)                                                                             0.1-2                                                                              bright                    7.   tin-zinc                                                                             n = 150                    vanillin                                                                              0.1-2                                                                              semi-bright                    plating bath                                                                         2 g/l                      (0.1 g/l)                                                                     propionaldehyde                                                               (0.1 g/l)                                                                     none    0.1-2                                                                              dull                                                             aldol                                                                         (0.5 g/l)                                                                             0.1-0.5                                                                            bright                                                           glyoxal                                            CH.sub.3O(NHC.sub.3 H.sub.7NH) .sub.n.sbsb.1 (CH.sub.2CH.sub.2                .sub.n.sbsb.2              (0.2 g/l)                              8.   tin-lead                          succin-                                     plating bath                                                                         n.sub.1 = 50               dialdehyde                                                                            0.1-0.5                                                                            semi-bright                           n.sub.2 = 50               (0.1 g/l)                                          2 g/l                      none    0.1-0.5                                                                            dull                                   ##STR15##                 piperonal (0.8 g/l)                                                                   1-4  bright                                                           glyoxal                                                                       (0.2 g/l)                              9.   tin-cobalt                                                                           n = 100                                                                plating bath                                                                         2 g/l                      none    1-4  semi-bright                            ##STR16##                 veratraldehyde (0.5                                                                   0.2-3                                                                              bright                    10.  tin-zinc                          anisaldehyde                                                                          0.2-3                                                                              bright                         plating bath                      (0.1 g/l)                                          n = 100                                                                       2 g/l                      none    0.2-3                                                                              semi-bright                            ##STR17##                 glyoxal (0.2 g/l)                                                                     0.1-2                                                                              semi-bright               11.  tin plating                       caproaldehyde                                                                         0.1-0.5                                                                            semi-bright                    bath                              (0.5 g/l)                                          n = 100                    none    0.2-3                                                                              dull                                  2 g/l                                                                         C.sub.3 H.sub.7NH(CH.sub.2CH.sub.2OH) .sub.n                                                             veratraldehyde                                                                        0.2-3                                                                              bright                                                           (0.5 g/l)                                          n = 150                    veratraldehyde                                     1 g/l                      (0.2 g/l)                                                                             0.2-3                                                                              bright                    12.  tin-zinc plating bath                                                                 ##STR18##                 anisaldehyde (0.2 g/l)                             n = 100                                                                       1 g/l                      none    0.2-3                                                                              semi-bright                           HO(CH.sub.2CH.sub.2OH) .sub.n                                                                            piperonal                                                                             0.1-2                                                                              bright                                                           (0.2 g/l)                                          n = 100                                                                       1 g/l                                                             13.  tin-cobalt plating bath                                                               ##STR19##                 p-tolualdehyde (0.1                                                                   0.1-2                                                                              bright                                n = 100                                                                       1 g/l                      none    0.1-2                                                                              semi-bright                           HO(CH.sub.2CH.sub.2O) .sub.n.sbsb.1(CH.sub.2CH.sub.2OH)                       .sub.n.sbsb.2              aldol                                                                         (0.5 g/l)                                                                             0.1-0.5                                                                            bright                                n.sub.1 = 20                                                      14.  tin-lead                                                                             n.sub.2 = 50               formaldehyde                                                                          0.1-2                                                                              semi-bright                    plating bath                                                                         1 g/l                      (0.2 g/l)                                           ##STR20##                                                                    n = 100                    none    0.1-2                                                                              dull                                  1 g/l                                                                                                    aldol   0.2-2                                                                              bright                                                           (0.2 g/1)                              15.  tin plating                                                                          EP-1                       anisaldehyde                                                                          0.2-2                                                                              bright                         bath   1 g/l                      (0.2 g/l)                                                                     none    0.1-2                                                                              semi-bright                                                      veratraldehyde                                                                        0.1-2                                                                              bright                                                           (0.5 g/l)                              16.  tin plating                                                                          EP-2                       acetaldehyde                                                                          0.2-2                                                                              bright                         bath   2 g/l                      (0.1 g/l)                                                                     none    0.2-2                                                                              semi-bright                                                      piperonal                                                                             0.2-2                                                                              bright                                                           (0.1 g/l)                              17.  tin-zinc                                                                             EP-3                       p-tolualdehyde                                                                        0.1-2                                                                              bright                         plating bath                                                                         2 g/l                      (0.1 g/l)                                                                     none    0.2-2                                                                              semi-bright               18.  tin-zinc                                                                             EP-4                       anisaldehyde                                                                          0.5-4                                                                              bright                         plating bath                                                                         1 g/l                      (0.2 g/l)                                                                     glyoxal                                                                       (0.1 g/l)                                                                     salicylaldehyde                                                                       0.2-4                                                                              bright                                                           (0.5 g/l)                                                                     none    0.5-4                                                                              semi-bright                                                      benzaldehyde                                                                          0.2-4                                                                              bright                                                           (0.2 g/l)                                                                     benzaldehyde                                                                  (0.1 g/l)                              19.  tin-silver                                                                           EP-5                       formaldehyde                                                                          0.5-4                                                                              bright                         plating bath                                                                         1 g/l                      (0.1 g/l)                                                                     none    0.2-4                                                                              semi-bright                                                      glyoxal 0.1-2                                                                              bright                                                           (0.2 g/l)                                                                     glyoxal                                20.  tin-zinc                                                                             EP-6                       (0.1 g/l)                                                                             0.1-2                                                                              semi-bright                    plating bath                                                                         2 g/l                      succindialdehyde                                                              (0.1 g/l)                                                                     none    0.1-2                                                                              dull                                                             veratraldehyde                                                                        0.2-4                                                                              semi-bright                                                      (0.5 g/l)                              21.  tin-cobalt                                                                           EP-7                       formaldehyde                                                                          0.5-4                                                                              bright                         plating bath                                                                         2 g/l (0.1 g/l)                                                                                          none    0.2-4                                                                              dull                                                             glyoxal                                                                       (0.2 g/l)                                                                             0.2-2                                                                              bright                    22.  tin-lead                                                                             EP-8                       formaldehyde                                                                          0.2-2                                                                              bright                         plating bath                                                                         2 g/l                      (0.2 g/l)                                                                     none    0.2-2                                                                              dull                                                             piperonal                                                                             0.2-2                                                                              bright                                                           (0.5 g/l)                                                                     anisaldehyde                                                                          0.1-2                                                                              bright                    23.  tin-zinc                                                                             EP-1 1 g/l                 (0.2 g/l)                                   plating bath                                                                         EP-3 1 g/l                 glyoxal                                                                       (0.1 g/l)                                                                     none    0.2-2                                                                              semi-bright                                                      veratraldehyde                                                                        0.2-4                                                                              bright                                                           (0.5 g/l)                              24.  tin-zinc                                                                             EP-2 1 g/l                 acetaldehyde                                plating bath                                                                         EP-5 1 g/l                 (0.1 g/l)                                                                             0.1-2                                                                              bright                                                           piperonal                                                                     (0.1 g/l)                                                                     none    0.2-4                                                                              semi-bright                                                      anisaldehyde                                                                  (0.2 g/l)                                                                             0.2-1                                                                              semi-bright                                                      aldol                                                                         (0.2 g/l)                              25.  tin-copper                                                                           EP-6 1 g/l                 propionaldehyde                                                                       0.2-1                                                                              semi-bright                    plating bath                                                                         EP-7 1 g/1                 (0.1 g/l)                                                                     none    0.2-1                                                                              dull                                                             anisaldehyde                                                                          0.5-4                                                                              bright                                                           (0.2 g/l)                              26.  tin-zinc                                                                             EP-4 1 g/l                 glyoxal                                                                       (0.1 g/l)                                   plating bath                                                                         EP-8 1 g/l                 salicylaldehyde                                                                       0.5-4                                                                              bright                                                           (0.1 g/l)                                                                     none    0.5-4                                                                              semi-bright               __________________________________________________________________________

We claim:
 1. An electroplating bath for depositing tin or a tin-alloy with brightness, characterized by adding to a tin or tin-alloy mother bath of a pH-value ranging from 4 to 8, which contains citric acid or its salt and an ammonium salt, a brightener comprising a water-soluble polymer selected from the group consisting of a polyoxyethylene, a derivative thereof and a reaction product of an epoxy compound with ethylene glycol, propylene glycol or glycerine.
 2. An electroplating bath as claimed in claim 1, further comprising an aldehyde compound as a co-brightener.
 3. An electroplating bath as claimed in claim 2, wherein the aldehyde compound is at least one selected from the group consisting of formaldehyde, acetaldehyde, propionaldehyde, glyoxal, succindialdehyde, caproaldehyde, aldol, benzaldehyde, p-tolualdehyde, salicylaldehyde, veratraldehyde, anisaldehyde, piperonal and vanillin.
 4. An electroplating bath as claimed in claim 3, wherein the aldehyde compound as co-brightener is added to the mother bath in an amount of 0.1 to 0.5 g/l.
 5. An electroplating bath as claimed in claim 1, wherein the polyoxyethylene or the derivative thereof is at least one compound selected from the group consisting of ##STR21## wherein n₁, n₂ and n₃ are integrals showing polymerization degree ranging from 20 to 200, from 10 to 100 and from 5 to 50, respectively.
 6. An electroplating bath as claimed in claim 5, wherein the polyoxyethylene or its derivative is added to the mother bath in an amount of 1 to 5 g/l.
 7. An electroplating bath as claimed in claim 1, wherein the epoxy compound is at least one selected from the group consisting of ##STR22## wherein R is a lower alkyl radical.
 8. An electroplating bath as claimed in claim 1, wherein the reaction product of the epoxy compound with ethylene glycol, propylene glycol or glycerine is added to the mother bath in an amount of 1 to 2 g/l. 